Hydrogen has long been proposed as an optimal fuel for transportation needs due to its abundance as well as its environmentally friendly properties. To date, the use of hydrogen as a fuel source has been limited by difficulties in providing adequate hydrogen storage capabilities, particularly for vehicular use. Heretodate, the primary methods of hydrogen storage involve storage as a compressed gas in pressurized tanks or utilizing low temperature storage as liquid hydrogen. Such storage mechanisms are impediments to vehicular use of hydrogen fuel, since high pressure and cryogenic storage technology are impractical for vehicular use. As a result, there have been extensive efforts to develop hydrogen storage systems using materials which offer the combination of high density hydrogen storage capabilities, favorable hydrogen dissociation kinetics, and using materials and processes having sufficiently low costs to be feasible for commercial transportation applications.
For instance, it is known in the art that the kinetics of hydrogen desorption from some alanates can be enhanced by doping an alanate such as sodium aluminum hydride with a transition metal. Sodium aluminum hydride has poor hydrogen storage kinetics and is reversible only under severe conditions of temperature and/or pressure change. Recently, it has been established that titanium doping of NaAlH4 can enhance the kinetics of hydrogen desorption and can provide for more moderate conditions for dehydriding. Work by Bodanovic and Schwickardi, as described in U.S. Pat. No. 6,106,801, and which is incorporated herein by reference, provides for titanium wet doping of NaAlH4 using an ether suspension have a 2 mole percent of titanium tetra-n-butoxide (Ti(OBu)4 However, the temperatures and kinetics of hydrogen adsorption and desorption of the doped material are such that the material still remains impractical for transportation applications.
U.S. Pat. No. 6,074,453 (assigned to Iowa State University Research Foundation, Inc.), incorporated herein by reference, discloses a method for making a hydrogen storage powder which is gas atomized under high temperatures and pressures to form generally spherical powder particles. The powder exhibits a small particle size which is stated to be resistant to microcracking during hydrogen adsorption/desorption cycling. However, the '453 reference utilizes hydrogen storage materials such as LaNi5 and other similar AB5 type materials which are too expensive for widespread use in transportation needs. Additionally, the resulting hydrogen storage powder set forth in the '453 patent requires substantial temperature and pressure variations in order to bring about useful adsorption and desorption cycles.
There remains a need for hydrogen storage materials that have a useful hydrogen storage capacity combined with low stringency release kinetics. Accordingly, there remains room for variation and improvement within the art of hydrogen storage materials.